Until now, deep wells have been lined with galvanized carbon steel screw joint pipes connected to each other by means of internally threaded couplings. The sealing function has been provided by flax or linseed oil. These pipes are heavy to handle since the depth of the well can be as much as 50 m and the wall of the pipe is thick. The thick pipe wall is needed in order to make room for the cut thread. Further, these screw joints have easily become disengaged due to the percussion and vibrations that occur during pumping.
Another well known pipe coupling for thin-walled pipes consists of a male portion and a female portion with matching threaded portions. The male portion has a conical enlargement axially inside the thread which is arranged to elastically force the cylindrical end portion radially outwards so as to make the coupling tightened during the final part of the in-screwing movement. This type of pipe coupling must be threadably engaged by means of machine force in order to provide sufficient force to the pipes so that an elastic deformation of the end portion of the female portion can occur. This end portion is also sensible to percussion.